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Are Pp and Ppk more useful than Cp and Cpk as a benchmark for further studies?

sushant_kulkarni

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#1
Hi,

Initial process capability values Cp & Cpk are use to predic long term process capability.

Pp & Ppk are used to process measures.

My question is in Pp sigma value we are taking is what population is.

where as Cp we are using sample sigma value.

As all of u know large population give ucorrect reading.

And each and every time u notice the things initial process capability allways

not appropriate.

so insteed of Cp & Cpk why not Pp & Ppk as a beach mark for further studies?

Bcoz they are appropriate.
 
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D

David DeLong

#2
Pp and Ppk values come from short term studies and one uses all the values. It reflects the process potential and, it high enough, determines whether long term statistical control is required. It determines whether your process can meet the specification and with a Pp and Ppk minimum value of 1.67 or 5 estimated standard deviation.

Cp and Cpk values come from your control charts with out of control situations that have been addressed not included in your data with the estimate of the standard deviation coming from the average range. This give one the true picture of the process over time. I guess you could state it is the score card of your process over time.
 
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